What is the definition of fracture-related infection?

Definition of Fracture-Related Infection

Fracture-related infection (FRI) is defined by specific diagnostic criteria established by the FRI Consensus Group, which categorizes features as either confirmatory (definitively indicating infection) or suggestive of infection. 1

Diagnostic Criteria for Fracture-Related Infection

Confirmatory Criteria (Definitive Diagnosis)

• Clinical Signs:

  • Presence of a sinus tract (fistula) communicating with the bone or implant 1
  • Wound breakdown exposing the bone or implant 1
  • Purulent drainage or presence of pus around the fracture site 1

• Microbiological Evidence:

  • Phenotypically indistinguishable pathogens identified from at least 2 separate deep tissue/implant specimens 1

• Histopathological Evidence:

  • Presence of microorganisms in deep tissue specimens confirmed using specific staining techniques for bacteria and fungi 1
  • Presence of >5 polymorphonuclear neutrophils per high-power field in chronic/late-onset cases (e.g., fracture nonunion) 1

Suggestive Criteria (Possible Infection)

• Clinical Signs:

  • Local or systemic signs such as pain, redness, swelling, or fever 1
  • New-onset joint effusion 1
  • Persistent, increasing, or new-onset wound drainage 1

• Laboratory Signs:

  • Increased serum inflammatory markers (ESR, WBC, CRP) 1, 2
  • A secondary rise after initial decrease or unexplained consistent elevation of inflammatory markers should increase suspicion of FRI 1

• Microbiological Evidence:

  • Pathogenic microorganism identified from a single deep tissue/implant specimen 1

Important Considerations in FRI Diagnosis

Time-Related Classification

• Historical classifications based on time (early, delayed, late-onset) exist but are considered arbitrary in current practice 1:
  • Willenegger and Roth classified FRIs as early (<3 weeks), delayed (3-10 weeks), and late-onset (>10 weeks) after fracture fixation 1
  • Other authors proposed a 6-week cutoff to differentiate between acute and chronic infections 1
  • Current consensus is that time-based cutoffs alone are not definitive for classification 1

Diagnostic Challenges

• The CDC criteria for surgical site infection capture less than 50% of FRIs requiring treatment, highlighting the importance of using FRI-specific diagnostic criteria 3
• Imaging findings such as implant loosening, bone lysis, failure of progression of bone healing, sequestration, and periosteal bone formation are suggestive but not confirmatory of FRI 1
• Individual serum inflammatory markers are only suggestive and not conclusive for FRI diagnosis 1

Multidisciplinary Approach

• A multidisciplinary team approach is recommended for diagnosis and management of FRI 4, 5
• Complex cases should be referred to specialized centers where multidisciplinary teams are available and physicians are experienced with FRI treatment 4

Pitfalls in FRI Diagnosis

• Relying solely on time-based classifications may lead to misdiagnosis 1
• Within the first 2 weeks after fracture fixation, the bone may not show signs of osteomyelitis despite bacterial presence on the implant 1
• Inflammatory markers may paradoxically increase within the first few weeks of diagnosis despite clinical improvement 2
• Overreliance on individual laboratory markers without clinical correlation can lead to misdiagnosis 1

The standardized FRI consensus definition has significantly improved the ability to diagnose these infections, with studies showing it captures 98.9% of infections occurring after operative fracture treatment, compared to less than 50% when using CDC criteria 3, 5.